Planetary transmission with a small tooth number difference has the advantages of large transmission ratio, small volume, high transmission efficiency, large bearing capability and the like, and has been widely used in the fields of metallurgy, mines, robots, aerospace and weapon equipment. The existing planetary transmission with a small tooth number difference has a constant transmission ratio. When the workload is changed and output rotation speed shall be adjusted to ensure the optimal operation state of the equipment, the rotation speed of a drive device is regulated in an electrical control manner to adapt to the change. This manner mainly relies on measurement and control, causing complex system structure and high cost. However, a self-adaptive mechanism realizes self-adaptive adjustment for external change operating conditions depending on self structural characteristics without measurement and control, and reliably completes expected working requirements. The current self-adaptive mechanism mainly includes some pressurization devices, holders, mechanical grippers, etc. composed of linkage structures and ordinary gears. A planetary transmission device with a small tooth number difference capable of realizing self-adaptation is absent.